For example, patent application FR 2 883 979 and U.S. Pat. No. 5,388,445 disclose methods of detecting peaks, i.e. wavefronts, in a time-varying signal based on windowing the signal, determining an indicator appropriate to the signal calculated in each window and a threshold, and comparing the indicator with the threshold, a wavefront being detected if the indicator exceeds the threshold. In U.S. Pat. No. 5,388,445, the indicator is a slope. In patent application FR 2 883 979 the indicator is the root-mean-square of the energy of the signal. The threshold employed for comparison depends on the indicator determined over windows preceding that in which the comparison is to take place. In a great number of situations those methods can detect the position of a wavefront in the signal, but no verification is effected to be sure that the detected wavefront corresponds to the looked-for event, which in the above documents is a partial discharge or a pressure transient. The detected wavefront could correspond to noise.
Furthermore, if the signal received by the detector is very noisy, the threshold may have an amplitude higher than the maximum amplitude of the signal, making detection impossible. Also, the looked-for wavefront cannot be detected if the signal received by the detector is subject to interference in the form of low-frequency noise, because it will have an amplitude lower than the maximum amplitude of the signal affected by the low-frequency noise. Thus with a single search for the occurrence of a wavefront it is not possible to be sure that a detected wavefront corresponds to the looked-for event.